The German priority document, DE 100 16 944.9, filed Apr. 9, 2000 is hereby incorporated by reference.
The invention relates to a method for reducing the moisture bound by capillary action in fiber cells in solids and/or sludges, especially raw brown coal, containing carbon, ground and screened to form a mat of outspread material, by the action of thermal energy and pressure on the input material that is to be dewatered, wherein the thermal energy comprising hot water and saturated steam and the mechanical energy as surface pressure on the input material is fed into and exercised on a pressure chamber of a filter press. The fiber cells may be cells of finely communited solid materials. The invention also relates to an apparatus for practicing that method. In the discontinuous embodiment, the spreading, loading and filtering belt passes through the press discontinuously in cyclical operation.
With regard to the former sieve method of processing the material to be dewatered, the principal application DE 199 40 392, which is hereby incorporated by reference, described the problem that the fine material screened out (fine material that exceeded the critical percentage of about 10%, up to about 35%, residual fine material content in the total material) could not be returned to the mechanical/thermal dewatering (MTE) process. The method and apparatus of the principal application addressed this problem.
In the apparatus according to the principal application, a disadvantage is found in the case of very great bulk weights, which results from the height of the hopper system for the coarse material. Because of the weight of the column of material coming from the high coarse material hopper (about 10 to 15 m high), the fine material layer (which comes from the fine material hopper) spread out underneath it is so greatly compressed (up to about 10 bar) that, as the process continues, the resistance to permeation by the process water and steam within the MTE pressure chamber is too high. When the height of the coarse material in the coarse material hopper is very high, the entire process is hindered.
There is an additional problem resulting from the high pressure in the material from the coarse material hopper. A controlled two-layer spread is no longer possible, because the entry of the fine material layer from the metal mesh belt is blocked in the direction of movement under the coarse material layer by the bulk material pressing down upon it from above.
The invention addresses the problem of improving the method and the apparatus according to the principal application DE 19940 392 such that the disadvantages set forth above are avoided and a trouble-free operation of the process is assured.
The solution regarding the method is achieved by the following process steps:
First, the input material is processed by grinding and screening the material and then feeding it into two spreader hoppers according to grain size and screened grain size distribution. The coarse material, thus separated, is fed to a first spreader hopper, and contains only a measured residue of fine material below the critical permeability limit. At the same time, the fine material, thus separated, with a grain size under 3 mm, is delivered to a second spreader hopper. Then, from the second spreader hopper (which precedes the first spreader hopper for the coarse material) a thin layer of fine material is spread onto a spreading, loading and filtering belt as a first layer. Then, from the first spreader hopper, a substantially thicker coarse material layer is drawn off by a transfer conveyor belt and then applied as a second layer over the fine material layer to form a xe2x80x9csandwichxe2x80x9d mat. Lastly the sandwich mat is brought by the spreading, loading and filtering belt into the MTE pressure chamber of the filter press for the dewatering cycle. Meanwhile, the pressed dry material is carried away.
The solution for the apparatus includes the following:
An arrangement of an input hopper and two material hoppers in tandem, wherein the material, already processed by grinding and screening, is fed as coarse material into a first spreader hopper. The screened-out fine material can be transferred over a chute and conveyor belt into a second spreader hopper, in which the fine material can be spread from the second spreader hopper onto the spreading, loading and filtering belt in a thinner layer, after passing through a vertically adjustable sliding gate. The coarse material can be transferred from the first hopper, initially onto a transfer belt running beneath it, and laid in a thick layer, after passing through a vertically adjustable gate, onto the fine material layer to form a sandwich mat of the outspread material.
The arrangement of a transfer belt for the coarse material is an advantage of the invention, whereby the entire weight of the bulk material column from the coarse material hopper is supported on the transfer conveyor belt. The necessary mass of material is controlled by the depth regulator, which depends on the bulk material depth and the final depth of the two-layer spread. Experiments have shown that, with a depth arrangement of HF and HC (fine material depth to coarse material depth) the method and apparatus herein described are advantageous.
The method and the apparatus according to the invention can be used both for a cyclic MTE process and for a continuous MTE process. Moreover, two embodiments could be used alternatively as continuous presses: the first is an embodiment similar to a continuously operating two-belt press with lateral pressure chamber walls between which an upper and lower endless metal mesh belt runs; the second embodiment is a roll press as a roll stand with a plurality of rolls arranged in tandem, which likewise are sealed off by corresponding lateral chamber walls to form a pressure chamber. In the first and second embodiments, the spreading, loading and filtering belt circulates both through the coarse and fine hopper system and through the pressure chamber.